The present invention is directed, in general, to a polishing apparatus and, more specifically, to a magnetic polishing head and retaining ring for polishing semiconductor wafers.
In the manufacture of microcircuit dies, chemical/mechanical polishing (CMP) is used to provide smooth topographies of the semiconductor wafers for subsequent lithography and material deposition. Briefly, the CMP process involves holding and rotating a thin, reasonably flat, semiconductor wafer while pressing the wafer against a rotating polishing surface or platen. The semiconductor wafer is held in a carrier that has a carrier ring about its periphery to restrain the wafer to a position under the carrier. The polishing surface is wetted by a chemical slurry, under controlled chemical, pressure, and temperature conditions. The chemical slurry contains selected chemicals which etch or oxidize specific surfaces of the wafer during processing. Additionally, the slurry contains a polishing agent, such as alumina or silica, which is used to abrade the etched/oxidized surfaces. The combination of mechanical and chemical removal of material results in superior planarization of the polished surface.
A polishing pad that rests on the surface of the polishing platen receives and holds the chemical slurry during polishing. Because of the extremely small tolerances necessary in semiconductor manufacture, it is important to maintain the planarity of the wafer.
Referring initially to FIG. 1, illustrated is a simplified, enlarged sectional view of a conventional carrier head and conventional polishing platen during polishing. As shown, a conventional carrier head 100 comprises a carrier body 110, a retaining ring 120, and a pneumatic interface 130. A conventional polishing surface 140 comprises a polishing platen 150, and a polishing pad 160. A semiconductor wafer 170 has a surface 172 being polished. One who is skilled in the art is familiar with the ripple 162 effect on the polishing pad 160 as the carrier head 100, semiconductor wafer 170, polishing platen 150, and polishing pad 160 rotate during polishing. In the illustrated embodiment, the free edge 121 contacted is on the retaining ring 120 that is being forced against the polishing pad 160 by a force 180 generated by the pneumatic interface 130. In addition to retaining the wafer 170 under the carrier head 100, the retaining ring 120 prevents the ripple 162 from contacting an outer edge 173 of the semiconductor wafer 170 and causing nonuniform polishing of the edge of the wafer 170. This nonuniform polishing at the edge 173 is known as the edge effect. As the pad 160 retains polishing slurry 190, any contact of the pad 160 with the wafer 170 will result in material removal from the wafer 170. In order to avoid the edge effect through contact with the ripple 162, the carrier ring 120 is extended toward the polishing pad 160, typically with pneumatic pressure, to cause the ripple 162 to form outward toward the circumference of the carrier ring 120 and away from the wafer 170. That is, a pneumatic interface 130 forces the retaining ring 120 against the pad 160 to form the ripple 162. The pneumatic interface 130 may be a relatively complicated system requiring pneumatic lines, seals and actuators (not shown) to assure the retaining ring 120 remains in contact with the polishing pad 160.
Accordingly, what is needed in the art is a simpler apparatus that eliminates the need to power an electromagnet in the polishing platen while still applying the necessary carrier ring force during chemical/mechanical polishing of semiconductor wafers.
To address the above-discussed deficiencies of the prior art, the present invention provides a polishing apparatus comprising a carrier head having a periphery, a first region, a carrier ring, and a second region. The carrier ring is coupled to the periphery. The carrier ring and carrier head are configured to cooperatively receive an object to be polished. The first region is associated with the carrier head and is capable of manifesting a polarity proximate the carrier ring. The second region is associated with the carrier ring and is capable of manifesting the same polarity proximate the first region. Therefore, the first and second regions have like polarities that create a repelling force between the carrier head and the carrier ring. The repelling force may be created by like magnetic fields or like electrostatic fields.
Thus, in one aspect, the present invention provides a polishing apparatus that has a polishing mechanism operable on the principles of magnetic or electrostatic forces that can be used to maintain a desired downward polishing force on a wafer.
In another embodiment, the first region is formed in the carrier head and the second region is formed in the carrier ring. The polishing apparatus, in an alternative embodiment, further comprises ring retainers interposed between the carrier head and the carrier ring. The ring retainers are configured to slidably couple the carrier head to the carrier ring.
In other embodiments, at least one of the first or second regions is a permanent magnetic region, a soft magnetic region, or an electromagnetic region. In a further aspect of this embodiment, the repelling force is adjustable by controlling a current in the electromagnetic region.
The polishing apparatus, in another embodiment, further comprises a drive motor coupled to the carrier head and configured to rotate the carrier head and the object, such as a semiconductor wafer. In one aspect of this embodiment, the polishing apparatus further comprises a polishing platen juxtaposed the carrier head and coupled to the drive motor configured to rotate the polishing platen. In an additional aspect, the polishing apparatus further comprises a polishing pad that is coupled to the polishing platen and that is configured to retain a polishing slurry. The polishing apparatus, in an another embodiment, further comprises a slurry delivery system in fluid communication with the polishing platen. The slurry delivery system is configured to deliver the polishing slurry to the polishing pad.
The foregoing has outlined, rather broadly, preferred and alternative features of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form.